Metal-over-metal devices and the method for manufacturing same

ABSTRACT

A metal-over-metal (MOM) device and the method for manufacturing same is provided. The device has at least one device cell on a first layer comprising a frame piece and a center piece surrounded by the frame piece. The center piece has a cross-shape center portion defining four quadrants of space between the frame and center pieces. The center piece has one or more center fingers each extending from at least one of the four ends thereof within a quadrant. The frame piece also has one or more frame fingers extending therefrom, each being in at least one quadrant and not being overlapped with the center finger in the same quadrant.

BACKGROUND OF THE DISCLOSURE

The present invention relates generally to semiconductor manufacturingprocesses, and more particularly, to a method and system for thefabrication of a metal-over-metal(MOM) device structure for integratedcircuit devices.

In integrated circuit design there are many applications ofhigh-performance, on-chip capacitors. These applications include dynamicrandom access memories, voltage control oscillators, phase-lock loops,operational amplifiers, and switching capacitors. Such on-chipcapacitors can also be used to decouple digital and analog integratedcircuits from the noise of the rest of the electrical system.

The development of capacitor structures for integrated circuits hasevolved from the initial parallel plate capacitor structures comprisedof two conductive layers, to trench capacitor designs, MOM designs andmore recently to the interdigitated metal finger structures. Theparallel plate capacitor is typically comprised of a first and secondlayer of conductive material patterned to define top and bottomelectrodes, with an intervening layer of a thin capacitor dielectric,the structure being isolated from the substrate by an underlyingdielectric layer of thick field oxide. The bottom electrode typicallycomprises a layer of conductive material, often polysilicon, which formsother structures of the integrated circuit, such as gate electrodes oremitter structures of transistors. The second (top) electrode is definedthereon by a second conductive layer, typically another polysiliconlayer. The capacitor dielectric is conventionally a thin silicon dioxideor silicon nitride layer. One of the well-known shortcomings of thisparallel plate capacitor structure is the relatively large area of thechip required for each device which makes it a less area-efficientstructure for advanced chip designs.

Trench capacitors are conventionally formed by depositing conductive anddielectric layers within trench regions defined in the substrate.Typically, an oval or circular vertical cylinder is etched into thesubstrate and concentrically arranged vertical electrodes are formedinside the trench. Trench capacitors exploit the downward verticaldimension into the substrate to create each capacitor device therebyreducing overall lateral dimensions of the chip which translates toreduced cost. A primary drawback to trench capacitors, however, is theirlack of scalability as feature sizes shrink. Economically etching thetrenches becomes difficult as the narrow trench openings and high aspectratios cause extended trench etch times limited by diffusion of theetching chemistry into and out of the trenches.

More recently, interdigitated finger capacitor structures have beendesigned which exploit both the lateral and vertical electric fieldsbetween the electrodes thereby creating higher capacitance values perunit area than previous capacitor designs. Unfortunately, these designshave structural limitations which makes them less desirable to utilizewithin design libraries and limit their flexibility within circuitdesigns.

What is needed is a method to provide a unit cell capacitor structurethat achieves high unit capacitance by exploiting both the lateral andvertical electric field components.

SUMMARY OF THE DISCLOSURE

To address the above discussed limitations in the prior art, the presentdisclosure provides a modular unit or cell for constructing ametal-over-metal (MOM) device and the method for manufacturing same. Inone embodiment, the MOM device may only have a single device layer. Thedevice has at least one device cell on a first layer comprising a framepiece and a center piece surrounded by the frame piece. The center piecehas a cross-shape center portion defining four quadrants of spacebetween the frame and center pieces. The center piece has one or morecenter fingers each extending from at least one of the four ends thereofwithin a quadrant. The frame piece also has one or more frame fingersextending therefrom, each being in at least one quadrant and not beingoverlapped with the center finger in the same quadrant.

In another example, a plurality of device layers are used, each beingseparated vertically by intervening layers of dielectric material. Inanother embodiment, the capacitor structure may be comprised of an arrayof the device cells, either on a single layer or a plurality of layers.

The MOM device can be easily integrated with aluminum or copper metalprocesses with no additional process steps. Additionally, the capacitorstructure will provide a plurality of layout and interconnect optionsintegratable into a process cell. Using such a MOM device as a capacitorbased device, high unit capacitance can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates one embodiment of the disclosure for one of the twolayers required to build a MOM or POP capacitor device.

FIG. 1B illustrates one embodiment of the disclosure for the second oftwo layers required to build a MOM or POP capacitor device.

FIG. 2A illustrates one embodiment for the via layout for the layerillustrated in FIG. 1A to connect one polarity parallel electrode to thesame polarity electrode in an upper or lower layer.

FIG. 2B illustrates one embodiment for the via layout for the layerillustrated in FIG. 1B to connect one polarity parallel electrode to thesame polarity electrode in a upper or lower layer.

FIG. 3A illustrates one embodiment for the via layout for FIG. 1A toconnect each polarity parallel electrode to the like polarity electrodein an upper or lower layer.

FIG. 3B illustrates one embodiment for the via layout for FIG. 1B toconnect each polarity parallel electrode to the like polarity electrodein an upper or lower layer.

FIG. 3C illustrates the overlay of via layouts for FIG. 1A and FIG. 1Bto connect each polarity parallel electrode to the like polarityelectrode in an upper or lower layer competing the a capacitor deviceunit cell.

FIG. 4 illustrates a device group array comprised of the unit celldevices.

DETAILED DESCRIPTION

A metal-over-metal (MOM) device and the method to manufacture same isprovided. Those skilled in the art should know that a plurality ofconductive materials may be used in the formation of the electrodes of acapacitor. Each electrode may be comprised of a different conductivematerial such as copper, aluminum, titanium nitride clad titanium, dopedpoly silicon, or another conductive material system. For simplicity,regardless of what specific type of metal is used, such a device isreferred to as a MOM device henceforth.

Referring initially to FIG. 1A, illustrated is one embodiment of asimple schematic view of a capacitor structure 100 according to oneexample of the present invention. The capacitor structure 100 includes afirst electrode 102, a dielectric layer 104, and a second electrode 106.As illustrated, the second electrode element 106 is formed by a framepiece, and the first electrode element 102 is formed by a center piece,surrounded by the frame piece, having a cross-shape center portion 108defining four quadrants of space between the frame and center piece. Ascan be seen, the center piece has four center fingers 110 each extendingfrom one of the four ends thereof within a quadrant. The frame piece 106also has four frame fingers extending therefrom and each being in onequadrant and not being overlapped with the center finger in the samequadrant.

It is understood that although the center portion, the center fingers,the frame piece, and the frame fingers are described as separateentities for illustration purposes, the center fingers and the centerportion can be formed as a single piece, and similarly, the framefingers and the frame piece can be formed as a single piece.

FIG. 1B illustrates a second embodiment of a schematic view of acapacitor structure 112 covered by the present invention. The capacitorstructure 112 includes a first electrode 114, a dielectric layer 104,and a second electrode 116. As illustrated, the second electrode element116 is formed by the frame piece, and the first electrode element 114 isformed by the center piece, surrounded by the frame piece, having across-shape center portion defining four quadrants of space between theframe and center piece. As can be seen, the center piece has four centerfingers each extending from one of the four ends thereof within aquadrant, and the frame piece has four frame fingers extending therefromand each being in one quadrant and not being overlapped with the centerfinger in the same quadrant. One having skill in the art knows thatinterconnects made to center piece and frame piece electrodes completethe formation of a planar capacitor structure in 100 and similarly in112. It is noticed that the structure shown in FIG. 1A is similar toFIG. 1B with the frame fingers and the center fingers arrangeddifferently. For illustration purposes, the structure in FIG. 1A isreferred to as a clockwise design and the one in FIG. 1B is referred toas a counter-clockwise design. As will be shown below, these twodifferent designs can be incorporated together in an MOM device

Furthermore, in order to achieve higher capacitance, structures 100 and112 may be stacked in a substantially vertical fashion in a plurality oflayers interconnected with one or a plurality of vias between theelectrode layers. It understood that when two metal layers arevertically aligned, if both of them are of either the clockwise orcounter-clockwise design, then, the via can be made at any location inthe center and frame pieces as they overlap in space, although separatedby the insulating layers. This would be the simplest design for stackingup metal layers to construct MOM devices.

Alternatively, metal plates of the clockwise and counter-clockwisedesigns can be stacked up alternately so that the center piece electrodecan be connected to the frame piece electrode. Having this capability isvery useful because external contacts can now all be made throughconnection on the frame pieces without having to have route through theframe piece to reach the hard-to-access center piece.

Referring to FIG. 2A and 2B illustrate via interconnect schemes on thecapacitor structure for connecting electrodes on different metal layers.The center piece electrode 102 is separated from the frame pieceelectrode 106 by the dielectric 104. Via locations 202 on the centerpiece 102 in layer 200 are interconnected to via locations 204 on theframe piece 110 in another layer 206 through an intervening layer ofdielectric 104 separating layers 200 and 206. Naturally, those havingskill in the art know that the dielectric material may be one ofseveral, such as silicon dioxide, silicon nitride, tantalum pentoxide,or a ferroelectric material. It is also well known that the dielectriclayer 104 may change in composition, thickness or both, from stackedlayer to stacked layer, depending on the process technology employed toconstruct the device. As shown, the capacitor in FIG. 2A is acounter-clockwise design and the one in FIG. 2B is a clockwise one. Itcan be seen that when stacking these together, the center piece in FIG.2A is connected to the frame piece in FIG. 2B. Since there is always aframe piece, to align them in production is very practical.

Referring now to FIG. 3A and 3B, capacitor structure 300 illustrates oneembodiment for a via interconnect scheme to capacitor structure 306 forboth polarity of electrodes. The center piece electrode 102 is separatedfrom the frame piece electrode 106 by the dielectric 104. Via locations202 on the center piece 102 in layer 300 are interconnected to vialocations 204 on the frame piece 110 in layer 306 through an interveninglayer of the dielectric 104 separating layers 300 and 306. In kind, vialocations 302 on the frame piece electrode 106 in layer 300 areinterconnected to via locations 304 on the center piece 108 in layer 306through an intervening layer of dielectric 104 separating layers 300 and306.

FIG. 3C is a top view showing the footprints of the stacked MOM device308. The layers 300 and 306 are stacked together vertically to comprisea substantially vertical capacitor structure. Via locations 310correspond to the interconnects of one polarity electrode of thecapacitor and via locations 312 correspond to the interconnects of thesecond polarity electrode of the capacitor structure.

What have been shown from FIG. 1A to FIG. 3C are only one modular unitof the capacitor. In the actual use, more than a single unit is needed.Turning next to FIG. 4, a stacked capacitor device group 400 is shownthat is made from individual unit cells 402. The units are arrayed inthree dimensions yielding a modular capacitor array design suitable forincorporation into a library of circuit design tools. FIG. 4 alsoillustrates the increase in packing density and lateral capacitanceachieved when the unit cell 308 is arrayed and the adjacent unit cellsshare a common inside unit cell perimeter edge.

When manufacturing a multilevel metal-over-metal (MOM) device group, oneor more MOM devices is initially formed on a first layer. Standard metalphotolithographical and etching or deposition processes are used. A CMPis applied to flatten the metal. A dielectric layer is then put on topof the first metal layer. Then, one or more MOM devices on a secondlayer are formed that are vertically aligned with the MOM devices on thefirst layer. The MOM devices the first and second layers are thenconnected so that portions of the devices on both layers having a samevoltage level are connected together.

As described and shown above, the device cell should be easily scaled,arrayed and incorporated eliminating requirements for additional DRC(design rule check) when implemented. They are compatible with standardintegrated circuit processing, require no additional processing steps.They are extremely suitable for fabrication with CMP (chemicalmechanical polishing) as each layer of metal can be separately processedand expected to be flat. Furthermore, the unit cell capacitor structureprovides the maximum interconnection flexibility for integration intocircuit design layouts.

While the invention has been particularly shown and described withreference to the preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention, as set forth in the following claims.

1. A metal-over-metal (MOM) device having at least one device cell on a first layer, each cell comprising: a frame piece; and a center piece surrounded by the frame piece having a cross-shape center portion defining four quadrants of space between the frame and center pieces; wherein the center piece has one or more center fingers each extending from at least one of the four ends thereof within a quadrant; wherein the frame piece has one or more frame fingers extending therefrom and each being in at least one quadrant and not being overlapped with the center finger in the same quadrant.
 2. The device of claim 1 wherein a first set of two center fingers being parallel to each other and extending towards a first and second opposite directions.
 3. The device of claim 2 wherein a second set of two extended center fingers being parallel to each other and extending towards a third and fourth opposite directions.
 4. The device of claim 3 wherein the frame finger is parallel with the center finger in the same quadrant.
 5. The device of claim 4 wherein the first and second sets of the center fingers are perpendicular to each other.
 6. The device of claim 4 wherein the center finger is perpendicular to a first portion of the cross shape center piece that it extends from.
 7. The device of claim 4 wherein the frame finger is situated on an inner side of the center finger so that it is closer to the center of the center piece.
 8. The device of claim 1 further comprising one or more connection points on the center and frame fingers of the device cell on the first layer connecting to at least one MOM device cell on a second layer vertically aligned therewith, wherein the center finger on the first layer connects to a frame finger of the MOM device cell on the second layer, and the frame finger on the first layer connects to a center finger of the MOM device cell on the second layer.
 9. The device of claim 1 wherein at least one side of the frame piece is connected to an external connection point.
 10. The device of claim 1 wherein the frame piece is at a first voltage level and the center piece is at a second voltage level.
 11. A multilevel metal-over-metal (MOM) device group having one or more MOM devices on a first layer connected to one or more MOM devices on a second layer, each of the MOM devices comprising: a frame piece; and a center piece surrounded by the frame piece having a cross-shape center portion defining four quadrants of space between the frame and center pieces, the center portion having a horizontal component and a vertical component; wherein the center piece has four center fingers each extending from one of the four ends thereof and being parallel to either the horizontal or the vertical component of the center portion, and wherein each quadrant has only one such center finger; wherein the frame piece has four frame fingers each extending from one side thereof, each being in one quadrant and being parallel with the center finger in the same quadrant.
 12. The device group of claim 11 further comprising one or more connection points on the center and the frame fingers for connecting each device on the first layer to at least one device on the second layer.
 13. The device group of claim 11 wherein a center finger extending from an end of the center portion of a first device on the first layer is in a different quadrant than the quadrant in which a center finger extending from a same end of center portion of a second device on the second layer connected with the first device.
 14. The device group of claim 13 wherein the center finger of the first device and the center finger of the second device extend in opposite directions.
 15. The device group of claim 13 wherein the frame piece of the first device and the center piece of the second device are on a first voltage level.
 16. The device group of claim 15 wherein the center piece of the first device and the frame piece of the second device are on a second voltage level.
 17. The device group of claim 13 wherein the frame finger is closer to the center of the cross-shape center portion than the center finger in the same quadrant.
 18. The device group of claim 12 wherein the frame fingers of the devices on the first layer connect to the center fingers of the devices vertically aligned therewith on the second layer through the connection points.
 19. The device group of claim 12 wherein the center fingers of the devices on the first layer connect to the frame fingers of the devices vertically aligned therewith on the second layer through the connection points.
 20. A method for manufacturing a multilevel metal-over-metal (MOM) device group, the method comprising: forming one or more MOM devices on a first layer; forming one or more MOM devices on a second layer that are vertically aligned with the MOM devices on the first layer; connecting the MOM devices on the first and second layers so that portions of the devices on both layers having a same voltage level are connected together; wherein each device having: a frame piece; and a center piece surrounded by the frame piece having a cross-shape center portion defining four quadrants of space between the frame and center pieces, the center portion having a horizontal component and a vertical component; wherein the center piece has four center fingers each extending from one of the four ends thereof and being parallel to either the horizontal or the vertical component of the center portion, and wherein each quadrant has only one such center finger; wherein the frame piece has four frame fingers each extending from one side thereof, each being in one quadrant and being parallel with the center finger in the same quadrant. 